[Three_thirty_I]

I suppose you can argue that, but you'll find that they will regard spark plugs as wear items. But, they do have an expected "lifespan" of 100k km or 60k miles, so depending on how far along they are and how much "life" they had left in them, you could suggest that the faulty coils reduced the lifespan of those spark plugs. But to be honest, spark plugs (unless you specifically go for OE) aren't that expensive, certainly not as expensive as the coils themselves.